Preprints  

Accurately dating ocean cores is challenging because the radiocarbon age of water masses vary substantially. We identify ash fragments from eruptions >4000 km from their source and use these time-markers to develop a new age-depth model for an ocean core in, Placentia Bay, North Atlantic. Our results show that the radiocarbon age of waters masses in the Bay varied substantially during the last 10,000 years and highlight the potential of using ultra-distal ash deposits in this region.

The Wasserstein distance is shown to be an appropriate dissimilarity metric for comparing distributional data such as detrital mineral ages. Using synthetic and real data we compare the Wasserstein distance to the commonly used Kolmogorov-Smirnov distance. The results are, in general, similar, but where they differ the Wasserstein distance is found to have more geologically sensible results. Code required to calculate the Wasserstein distance between distributions is provided in python and R.

Volcanic ash layers are a common tool to synchronize records of past climate, and their estimated age relies on external dating methods. Here, we show that the chemical composition of the well-known, 12000 year-old Vedde Ash is indistinguishable with several other ash layers in Iceland that are ~1000 years younger. Therefore, chemical composition alone cannot be used to identify the Vedde Ash in sedimentary records.

(U-Th)/He dating relies on proper characterization of apatite crystal dimensions so that eU concentrations and dates can be calculated accurately and precisely, but there is systematic error and uncertainty on geometric measurements. By comparing 2D microscopy to “true” 3D measurements, we present a simple solution to correcting the error and quantifying the geometric uncertainty on eU and dates. Including this geometric correction and uncertainty matters for data evaluation and interpretation.

We report aspartic and glutamic acid racemization analyses on Neogloboquadrina pachyderma and Cibicidoides wuellerstorfi from the Arctic Ocean (AO). The rates of racemization in the species are compared. Calibrating the rate of racemization in C. wuellerstorfi for the past 400 ka allows the estimation of sample ages from the central AO. Estimated ages are older than existing age assignments (as previously observed for N. pachyderma), confirming that differences are not due to taxonomic effects.

The Great Unconformity represents an enormous amount of time lost from the sedimentary record. Its origin is debated, in part, due to different approaches used to interpret zircon (U–Th)/He ages. This thermochronometric system is ideal for this problem because the temperature sensitivity varies according to radiation damage. Here we explore the uncertainty associated with the radiation damage model and show how this limits our ability to resolve the origin of the Great Unconformity.

When using the uranium-lead radiometric dating method on very young materials (e.g. Quaternary age zircon and carbonate minerals), it is important to accurately account for the production and decay of intermediate ‘daughter’ isotopes in the U-series decay chain. DQPB is open-source software that allows users to easily make such corrections for a variety of sample types and to produce publication-ready graphical outputs of the resulting age information.

We present our model ChronoLorica. We coupled the original Lorica model, that simulates soil and landscape evolution, with a geochronological module that traces cosmogenic nuclide inventories and particle ages through the simulations. These properties are often measured in the field to determine rates of landscape change. The coupling enables calibration of the model and study how soil, landscapes and the geochronometers change under complex boundary conditions such as intensive land management.

Thermochronometric data can provide unique insights into the patterns of rock exhumation and the driving mechanisms of landscape evolution. Several well-established thermal models allow for a detailed exploration of how cooling rates evolved in a limited area or along a transect, but more regional analyses have been problematic. We present age2exhume, a thermal model that can be used to rapidly provide a synoptic overview of exhumation rates from large regional thermochronologic datasets.

Sediment cores from volcanic lake Holzmaar provide a very precise chronology based on tree ring-like annual laminations or varves. We statistically combine this varve chronology with radiometric dating and tested three different methods to upgrade the age-depth model. However, only one of the three methods tested improved the dating accuracy considerably. With this work, an overview of different age-integration methods is discussed and made available for increased future demands.

Absolute chronological constraints are crucial in Earth and Planetary Science. In recent years, U-Pb dating of calcite has provided information on the timing of diagenesis, faulting, or hydrothermalism, for example. These studies have targeted relatively young carbonates up to 300 million years old. By dating 3.9 billion years old martian carbonates using the U-Pb chronometer, we show that this system can be robust in ancient samples that have had a relatively simple history.

SHRIMP (Sensitive High Resolution Ion MicroProbe) is a instrument that for decades has used the radioactive decay of uranium into lead to measure geologic time. The accuracy adn precision of this instrument has not been seriously reviewed in almost 20 years. This paper compares several dozen SHRIMP ages in our database with more accurate and precise methods to assess SHRIMP accuracy and precision. Analytical and geologic complications are addressed to try to improve the method.

If topographical obstructions are present in the surroundings of sampling sites, exposure ages of rock surfaces need to be corrected. A toolbox for the ESRI ArcGIS software allows for quantifying topographic shielding with a digital elevation model, but it has only been validated with few field data. In this study, the output of the toolbox is evaluated with a more extensive dataset. If suitable elevation data is chosen, the toolbox provides a sound approach to determine topographic shielding.

Acid leaching is commonly used to remove damaged portions of zircon crystals prior to U-Pb dating. However, a basic understanding of the microstructural processes that occur during leaching is lacking. We present the first 3D view of zircon dissolution based on X-ray computed tomography data acquired before and after acid leaching. These data are paired with images of etched grain surfaces and Raman spectral data. We also reveal exciting opportunities for imaging radiation damage zoning in 3D.

In situ ¹⁴C’s short half-life (5.7 ky) is unique among cosmogenic nuclides, making it sensitive to complex exposure/burial histories since 25 ka. Current extraction methods focus on quartz, but the ability to extract it from other minerals would expand applications. We developed MATLAB^® scripts to calculate in situ ¹⁴C production rates from a broad range of mineral compositions. Results confirm O, Si, Al, and Mg as key targets, but also find significant production from Na for the first time.

Deposits left behind by past glacial activity provide insight into the previous size and behavior of glaciers, and act as another line of evidence for past climate. Here we present new age control for glacial deposits in the mountains of Montana and Wyoming, United States. While some deposits indicate glacial activity within the last 2000 years, others are shown to be older than previously thought, thus redefining the extent of regional Holocene glaciation.

We constrained deposition phases of fluvial sediments (NE Belgium) over the last 1 Ma with analysis and modelling of rare isotopes accumulation within sediments, occuring in function of time and inverse function of depth. They allowed the determination of 3 superposed deposition phases and intercalated non-deposition periods of ~ 40 kyr each. These phases correspond to 20% of the sediment age, which highlights the importance to consider deposition phase when dating fluvial sediments.

There is currently no standardized method of performing uncertainty propagation in the (U-Th)/He system, causing difficulties in data interpretation. We present two methods of uncertainty propagation and describe a free, open-source software (HeCalc) to apply these methods. A compilation of real data using only analytical uncertainty, and 2 % and 5 % uncertainties in F_T yields respective median relative date uncertainties of 2.9 %, 3.3 % and 5.0 % for apatites and 1.7 %, 3.3 % and 5.0 % for zircons.

We developed code to automatically and semi-automatically measure dimensions of detrital mineral grains in reflected light images saved at LA-ICP-MS facilities that use Chromium targeting software. Our code uses trained deep learning models to segment grain-images with greater accuracy than is possible using other image segmentation techniques. We implement our code in user-accessible, ready-to-run Google Colab notebooks, links to which can be found at https://github.com/MCSitar/colab_zirc_dims.

We proposed a new non-destructive mineralogical methodology on inframilimetric grains that allows to quantify the hematite and goethite content and hematite/goethite ratio of grains prior to (U-Th)/He geochronological analysis. (U-Th)/He data performed on different aliquots with different acquisition time shows no remarkable differences in age, opening a new way to investigate the (U-Th)/He data evolution in supergene lateritic duricrusts.

Chemical weathering alters the chemical composition of mineral grains, and it follows that luminescence dating signals may also be progressively modified. We artificially weathered feldspar samples under different chemical conditions to understand the effect of feldspar partial dissolution on their luminescence properties. Only minor changes were observed on luminescence dating properties, implying that chemical alteration of feldspar surfaces may not affect luminescence dating signals.

This paper outlines a method that helps mineral explore for gold. When can see the alteration caused by the mineralising fluids, it is possible to use geochemical methods to vector towards the deposit. But such methods failed at Martabe. We decided to work out why. Our results showed that there were several distinct and separate very short-lived alteration events. The answer might be that vectoring is possible only when samples are compared from the same mineralising system.

Paleomagnetic data from Cascade Lake (Brooks Range, Alaska) extend the radiometric-based age model of the sedimentary sequence extending back 21 kyr. Correlated ages based on prominent features in paleomagnetic secular variations (PSV) diverge from the radiometric ages in the upper 1.6 m, by up to about 2000 years at around 4 ka. Four late Holocene cryptotephra in this section support the PSV chronology and suggest the influence of hard water or aged organic material.

Prehistoric volcanic eruptions are often dated by wiggle matching series of radiocarbon ages on tree rings to standard calibration curves, ignoring potential contamination by 'old' carbon given off by the volcano. We modeled the effects of low amounts of contamination on wiggle match dates for the 10th century Changbaishan eruption and found evidence of contamination in all. We propose a new protocol to identify the presence of contamination, and provide more secure dates for major eruptions.

The timing and duration of fluid activity within a gold deposit enables a greater understanding of how the deposit evolved and thus help future mineral exploration. This research uses high resolution dating methods to unravel the overprinting fluid activity at the Martabe gold field in Sumatra. Methods outline in this report can be applied to deposits globally.

Potassium-based geochronology, including the ⁴⁰Ar/³⁹Ar and K-Ar methods, provides critical constraints on the timing and duration of many events and processes in earth history. These methods assume that a key parameter, the fraction of potassium with a mass of 40, does not vary in some relevant materials. Some recent work has identified some variability in these materials. This work examines the effects of this variability on calculated K-Ar and ⁴⁰Ar/³⁹Ar ages.